This application is based upon claims the benefit of priority from the prior Japanese Patent Application No. 11-320453 filed Nov. 11, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a signal analyzing apparatus and, more particularly, to a signal analyzing apparatus that measures the frequency characteristics of signals used in mobile communication systems such as mobile telephones and cellular telephones and displays their waveforms.
For example, signals employed in mobile communication systems such as mobile telephones and cellular telephones are modulated by a number of modulation methods.
These mobile communication systems adopt TDMA (Time Division Multiple Access) as a communication method for using communication circuits efficiently.
The frequencies of carrier waves conveying signals used in those mobile communication systems are very high, ranging from several hundred MHz to several GHz.
Signal analyzing apparatuses such as spectrum analyzers are used to precisely measure various frequency components included in those signals.
FIG. 3 is a block diagram that illustrates a schematic configuration of the prior-art signal analyzing apparatus that measures the frequency characteristics of such signals of high frequencies.
In such a conventional signal analyzing apparatus 51 of FIG. 3, signal xe2x80x9caxe2x80x9d of a high frequency that is entered through an input terminal 52 for decoding is controlled to have a predetermined level of intensity with an attenuator (ATT) 53 and then provided to a frequency conversion unit 54.
The signal of a high frequency entered to the frequency conversion unit 54 for decoding is mixed in a signal mixer 55 with a local oscillation signal xe2x80x9cbxe2x80x9d transmitted from a local oscillator 56 and then converted to a signal of an intermediate frequency.
The signal of an intermediate frequency is narrowed in bandwidth with a BPF (Band Pass Filter) 57 and again mixed with the local oscillation signal transmitted from the local oscillator 59 in another signal mixer 58 in the subsequent part and sent out from the frequency conversion unit 54.
The frequency provided by the local oscillator 56 in the frequency conversion unit 54 is swept over a predetermined frequency range by a sweep control unit 60.
As a result, the frequency of the intermediate-frequency signal xe2x80x9ccxe2x80x9d sent out from the frequency conversion unit 54 changes in synchronization with the sweeping operation.
The intermediate-frequency signal xe2x80x9ccxe2x80x9d of which frequency was reduced and sent out from the frequency conversion unit 54 is entered to a Resolution BAND Width (RBW) filter 61.
This RBW filter 61 is comprised of an analog band pass filter having frequency characteristics shown in FIG. 4, for example, and only selects necessary signals of intermediate frequencies with unnecessary frequency components being removed.
The bandwidth (RBW) 3 dB lower than the peak level of the central passing frequency fc in the frequency characteristics of the band pass filter represents the frequency resolution of this signal analyzing apparatus 51.
Frequency f1 of the intermediate-frequency signal xe2x80x9ccxe2x80x9d sent from the frequency conversion unit 54 changes in synchronization with the sweeping operation.
Therefore, the output signal sent out from the RBW filter 61 during a one sweeping period (sweeping interval) present the time-series waveform of each frequency component in the measurement signal xe2x80x9caxe2x80x9d that has been converted to the intermediate-frequency signal xe2x80x9ccxe2x80x9d.
This output signal from the RBW filter 61 is log-converted by a logarithmic (LOG) converter 62 after a gain adjustment in an amplifier (not shown).
The output signal, of which signal level has been converted by the dB, is decoded in a detector (DET) 63 in the following part.
Consequently, the signals swept by DET63 during the sweeping interval represent the amplitudes of the time-series waveforms of the swept frequencies.
Therefore, the output signals from the detector 63 represent frequency spectrum waveforms, when plotted along with a horizontal axis of frequency and a vertical axis of amplitude.
The signals provided from the detector 63 that represent frequency spectrum waveforms are entered to an analog Video BAND Width (VBW) filter (not shown).
This VBW filter is comprised of a low pass filter (LPF) that removes high-frequency components (noise) in the frequency spectrum waveforms to be shown in a display unit 64 that is installed on the front panel of the apparatus.
A peak detector (not shown) detects the peak of the analog frequency spectrum waveform provided from the VBW filter at each position on the time axis and the final frequency spectrum waveform is obtained that is envelope-detected.
Signals presenting the final frequency spectrum waveforms are converted into digital data in an A/D converter 65 that is installed in the following part.
These frequency spectrum waveforms converted into digital data are displayed on the screen of the display unit 64 mounted on the front panel.
Changing the display frequency range on the display unit 64 and sweeping frequency range, frequency spectra over a wide range of frequency and in an arbitrary frequency range can be provided for measurement.
Further, if the bandwidth (RBW) of the RBW filter 61 is changed, the frequency resolution of the signal analyzing apparatus 51 can be changed.
In general, a wider sweeping range leads to a wider bandwidth (RBW) and a lower wavenumber resolution.
Namely, the bandwidth (RBW) of the RBW filter 61 depends on changes in the sweeping frequency range.
For higher productivity in signal measurement, the throughput of tuning and inspection in such signal analyzing apparatuses should be raised.
One of the improvements is to reduce measurement time and another is to raise the sweeping seed.
In signal analyzing apparatuses such as conventional spectrum analyzers, since the minimum sweeping time is around 20 ms, the magnitude of delay is not important.
Signal analyzing apparatuses such as modern spectrum analyzers conduct high speed sweeping by raising the sweeping rate in the local oscillator.
However, in the prior-art signal analyzers shown in FIG. 3, a high-speed sweeping causes a delay in the response of signals upon data sampling in the A/D converter 65 because of a group delay time that is induced in devices ranging from the signal mixer 58 to the A/D converter 65 to which local oscillation signals are entered.
In particular, in the case of a high-speed sweeping conducted in the configuration of FIG. 3, delay occurs on the way to the A/D converter 65 due to the delay characteristics of the analog RBW filter 61, and such delay increases if RBW (bandwidth) of the RBW filter 61 becomes narrow.
Such time delays appear as shifts in the frequency position when waveforms are shown in the display unit 64.
Namely, as demonstrated in FIG. 5, the peak position that should be located at the central frequency fc shown by the solid line moves to a position, fcxe2x80x2, shown by the dotted line, causing an error display of frequency. Correct signal analysis thus becomes difficult to perform.
This invention has been made to solve the above problems, and the object of the invention is, in particular, to provide a signal analyzing apparatus that can perform precise signal analysis by reducing frequency errors induced in high-speed sweeping.
To achieve the above object, according to the first aspect of the present invention, there is provided a signal analyzing apparatus comprising:
a frequency conversion unit (4) that converts input signals into those of intermediate-frequencies using a predetermined local oscillation frequency;
a sweeping unit (12) that sweeps the local oscillation frequency in a predetermined sweeping time;
a filter (10) that receives signals output from the frequency conversion unit and selectively passes signals having frequency components of a predetermined bandwidth;
an A/D conversion unit (16) that samples the signals that have passed the filter and converts them into predetermined digital data;
a data storage unit (17) that saves the digital data converted by the A/D conversion unit;
a signal processing unit (18) that conducts signal processing, extending the digital data saved in the data storage unit into frequency spectrum data;
a correction data storage unit (20) that saves correction data representing delay times for the bandwidth of the filter;
a control unit (11) that causes the signal processing unit to process signals so that a measured frequency corresponding to the local oscillation frequency for starting sweep in the sweeping unit and the digital data corresponding to the measured frequency saved in the data storage unit may be processed in a one-to-one relationship in the signal processing unit by changing the timing at which data is sent from the A/D conversion unit to the signal processing unit via the data storage unit based on the correction data saved in the correction data storage unit; and
an output unit (19) that outputs the frequency spectrum data which has been processed in the signal processing unit.
Also to achieve the above object, according to the second aspect of the present invention, there is provided a signal analyzing apparatus comprising:
a frequency conversion unit that converts the frequencies of input signals into intermediate-frequencies;
a sweeping unit that sweeps the frequencies of the intermediate-frequency signals that are outputted by changing local oscillation frequencies in the frequency conversion unit, for a predetermined sweeping time;
a filter that receives the intermediate-frequency signals output from the frequency conversion unit and selectively passes the frequency components of a predetermined bandwidth;
an A/D conversion unit that converts the signals that have passed the filter into digital data with number of points based on a predetermined sampling frequency;
a data storage unit that saves the digital data converted by the A/D conversion unit;
a signal processing unit that conducts signal processing, extending the digital data saved in the data storage unit into frequency spectrum waveforms;
a display unit that displays the frequency spectrum waveforms processed in the signal processing unit; and
a control unit that causes the data storage unit to save a plurality of sets of digital data converted by the A/D conversion unit, more than number of display data points displayed in the display unit, in the data storage unit, and enter a readout initiation position in the data storage unit to the signal processing unit with a correction of number of points corresponding to delay times due to the filter.
Also to achieve the above object, according to the third aspect of the present invention, there is provided a signal analyzing apparatus comprising:
a frequency conversion unit that converts the frequencies of input signals into intermediate-frequencies;
a sweeping unit that sweeps the frequencies of the intermediate-frequency signals that are outputted by changing local oscillation frequencies in the frequency conversion unit, for a predetermined sweeping time;
a filter that receives the intermediate-frequency signals output from the frequency conversion unit and selectively passes signals having frequency components of a predetermined bandwidth;
an A/D conversion unit that converts the signals that have passed the filter into digital data;
a data storage unit that saves the digital data converted by the A/D conversion unit;
a signal processing unit that conducts signal processing, extending the digital data saved in the data storage unit into frequency spectrum waveforms;
a display unit that displays the frequency spectrum waveforms processed by the signal processing unit; and
a control unit that delays data acquisition timing in the data storage unit as long as delay time induced in the filter.
Also to achieve the above object, according to the forth aspect of the present invention, there is provided a signal analyzing apparatus comprising:
a frequency conversion unit that converts frequencies of input signals into intermediate-frequencies;
a sweeping unit that sweeps frequencies of intermediate-frequency signals that are outputted by changing local oscillation frequencies in the frequency conversion unit, for a predetermined sweeping time;
a filter that receives the intermediate-frequency signals output from the frequency conversion unit and selectively passes signals having the frequency components of a predetermined bandwidth;
an A/D conversion unit that converts the signals that have passed the filter into digital data;
a data storage unit that saves the digital data converted by the A/D conversion unit;
a signal processing unit that conducts signal processing, extending the digital data saved in the data storage unit into frequency spectrum waveforms;
a display unit that displays the frequency spectrum waveforms processed in the signal processing unit;
a correction data storage unit that saves the data indicating delay times due to the filter; and
a control unit that calculates delay times of signal till through the A/D converter, based on sweeping time for one point in sampling by the A/D converter and the correction data saved in the correction data storage unit, further calculates readout initiation position in the data storage unit from this calculated delay time, and enters the calculation results into the signal processing unit;
wherein the signal processing unit reads out digital data sequentially starting from the readout initiation position calculated by the control unit and outputs the digital data, extending into frequency spectrum waveforms after signal processing.
Further to achieve the above object, according to the fifth aspect of the present invention, there is provided a signal analyzing apparatus comprising:
a frequency conversion unit that converts the frequencies of input signals into intermediate-frequencies;
a sweeping unit that sweeps frequencies of the intermediate-frequency signals that are outputted by changing local oscillation frequency in the frequency conversion unit, for a predetermined sweeping time;
a filter that receives the intermediate-frequency output signals from the frequency conversion unit and selectively passes signal having frequency components of a predetermined bandwidth;
an A/D conversion unit that converts the signals that have passed the filter into digital data;
a data storage unit that saves the digital data converted by the A/D conversion unit;
a signal processing unit that conducts signal processing, extending the digital data saved in the data storage unit into frequency spectrum waveforms;
a display unit that displays the frequency spectrum waveforms processed in the signal processing unit;
a correction data storage unit that saves the data indicating delay times due to the filter;
a delay circuit inserted for use in the input of timing for data acquisition in the data storage unit; and
a control unit that calculates delay times for the bandwidth of the filter saved in the correction data storage unit and controls delay times of the delay circuit so that it matches the calculated delay time;
wherein the timing for data acquisition from the data storage unit is delayed as long as the delay time in the delay circuit.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.